This invention relates to color printing, and more particularly to minimizing color hue shift in bidirectional color inkjet printing.
The art of inkjet printing technology is relatively well developed. Commercial products such as computer printers, graphics plotters, copiers, and facsimile machines employ inkjet technology for producing hard copy printed output. The basics of this technology are disclosed, for example, in various articles in the Hewlett-Packard Journal, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988) Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45 No. 1 (February 1994) editions. Inkjet devices are also described by W. J. Lloyd and H. T. Taub in Output Hardcopy Devices, chapter 13 (Ed. R. C. Durbeck and S. Sherr, Academic Press, San Diego, 1988).
With the increased popularity of inkjet printing comes the increased competition between manufacturers of inkjet printers. Currently, the most common distinguishing features between competitive inkjet printers are price, speed, and print quality. Today, most inkjet printer manufacturers sell a model of printer in each price range of inkjet printers ranging from low cost home and office printers to high-speed commercial printers. To be competitive within each price range, the printer manufacturer must supply a printer with a faster print speed and a better resultant print quality than his competitors"". With price at a consistent low among the competitive inkjet printer manufacturers, a fast print speed directly coupled to a superior resultant print quality is key to the consumer""s selection.
In the inkjet printing systems of today, color is mapped between that viewed on the monitor or display in a RGB (Red, Green, Blue) format to that outputted on an inkjet printer in a CMY (Cyan, Magenta, Yellow) format. This color mapping is necessary to obtain the xe2x80x9ctruexe2x80x9d colors the user expects based on the display of color on the monitor as the mixing of the three colors are different between RGB and CMY schemes. U.S. Pat. No. 5,704,021 to Smith et al., assigned to the same Assignee as the present invention, discloses the process of xe2x80x9ccolor mappingxe2x80x9d in color inkjet printers.
Color mapping provides the printer driver with the combination and amount of color ink droplets to be applied to the outlet to get the requested color. However, due to the fixed order of the color print cartridges in the printer, the order in which the ink droplets are to be applied is fixed. For example, in an inkjet printer where the print cartridges are ordered from left to right, a combination of Cyan and Yellow will have to be ordered Yellow then Cyan. In the event the inkjet printer works in a bi-directional mode, when returning in the right to left direction, a combination of Cyan and Yellow will have to be ordered Cyan then Yellow. This typically creates a varying color between left to right passes and right to left passes of the print cartridges. This variation may produce an undesirable banding effect to the output.
The fastest way to print a contiguous area of color with a scanning inkjet printhead is to sweep the printhead across the media in a first direction while firing ink droplets as prescribed by the color map from an array of nozzles, advance the media the height of the array of nozzles then sweep the printhead in a second, opposite direction firing ink droplets as before. This is known as single-pass, bi-directional printing. Single-pass because the printhead passes over each area of the page only one time. There is minimal or no overlap between adjacent printed rows. Bi-directional because drops are fired while the printhead is travelling in both the left to right direction and the returning right to left direction.
This technique is well known and successful for printing in monochrome. Workers skilled in this field have recognized, however, that for printing in color a hue shift, or more precisely a color hue shift, arises between printing left to right over right to left.
One solution to this problem has been to digress to single-pass unidirectional printing In this case, everything is printed in a left to right order, thereby eliminating the directional related color hue shifts. A second solution to the problem is to resort to multi-pass bi-directional printing where the colors arc overlayed in an averaging or blending scheme whereby the banding becomes less noticeable. Either of these two solutions compromise print speed to achieve highest print quality.
A third solution is proposed in the aforementioned concurrently filed application, titled xe2x80x9cA Method for Minimizing Hue Shifts in Single-Pass, Bi-Directional Color Inkjet Printing,xe2x80x9d in the name of Ross et al.
In the competitive inkjet market of today where the users command faster, smaller, less expensive, high quality inkjet printing, the addition of two print cartridges both increases the cost of manufacture as well as the size of the printer enclosure necessary to house these additional print cartridges.
With the increasing use of inkjet printers for high quality color printing in the home and in the office, there is a need for a high speed, low cost, compact inkjet printer that produces a uniform high quality output.
A single-pass printer prints in a first direction and a second direction on a print medium. The second direction is opposite the first direction. The printer has a first color map and a second color map. The printer has a print mode which employs the first color map while depositing a first swath of ink droplets onto the print medium in the first direction, and employs the second color map while depositing a second swath of ink droplets, adjacent to the first swath of ink droplets, onto the print medium in the second direction.